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Why should I remove furniture before taking room correction measurements?

richard12511

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#1
I asked this in another thread, but didn't really get any response. I've seen some very knowledgeable folks(including @mitchco) suggest that removing furniture (like couches, foot rest tables, etc.) will lead to superior room correction results. Dirac also says to make sure there is nothing(like a couch back) close(within 12inc) to the mic when taking measurements. This seems to imply removing the couch, too. Who listens on a couch with their head more than 12 inches away from the back of the couch?

However, this doesn't make logical sense to me. As @Chromatischism pointed out, by removing furniture before taking measurements, aren't I essentially lying to Dirac about the characteristics of my room(and what it needs to correct for)?
 

RayDunzl

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#2
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#3
No, you definitely want to do your measurements with all the furniture in the normal places you will listen later. You should make sure that nothing is blocking direct sound from your speakers to where your ears will be. That may not be 100% possible, so minimize where it's not (an ottoman, say). Dirac's instructions are just trying to minimize any reflections that are close to your head. I'm guessing the back of your couch isn't as high as your head, but if it is, just work with it. You want those first several mic spots to be close to where actual listeners' ears will be. Good luck.
 

Robbo99999

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#5
Yes Richard, that doesn't make sense to me either, I imagine all the furniture (indeed everything in your room) will have an effect on the measurement & indeed the sound you hear, so to measure it in an empty room sounds absurd. Unless, if I use my imagination, the plan is that it's gonna be a dedicated listening room and you're taking a base measurement of the sound of the room without furniture, at which point you could introduce furniture to see it's subsequent effect on further measurements - as a means of choosing optimum furniture & positioning for your listening room ha, but who wants to live like that!! Hell you could sit on a little foldaway chair in the middle of your empty room & enjoy your music - a bit like a solitary trip to the bathroom for ablution purposes!!
 

mitchco

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#7
@richard12511 as mentioned in the other thread... Also, folks need to read a little closer :) Where does it that I say move everything out of the room? LOL! Attention to details matter.

The idea is not to move the furniture out of the room, it is to move anything between the mic and speakers out of the way that can cause comb filtering and anything around the microphone itself, like comb filtering off the chair/couch for example. We are concerned with midrange and high frequency comb filtering as the wavelengths are so long below 100 Hz that it does not have a real impact with objects in the way...

The fundamental issue is if one corrects for the “comb filtering” off the coffee table for example, then that correction is now embedded in the frequency response of the loudspeaker including it's off axis response. So if we correct for the comb filter off the coffee table, we have just coloured the off axis response of the loudspeaker. Here is a longer answer: https://audiophilestyle.com/forums/...kthrough/page/2/?tab=comments#comment-1032876

As mentioned in the link, recording, mixing and mastering engineers deal with this daily with mixing desks, etc. Mastering engineer Bob Katz has a nice comparison of the comb filtering he was getting at his mixing desk and found a unique to deal with it, including before and after measurements in his mastering book. It is a well known issue in studio world...

Why not try the try the experiment yourself, if you haven't already, and then compare the filters (measurement and listening) see which is better and report back.
 

Robbo99999

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#8
So @mitchco , it's more in the context of intelligent room design as a whole, in terms of placing furniture optimally or sensibly to avoid issues.....so it's not about vacating the room of furniture. I mean that makes sense. The problem arises when you can't or don't want to move certain items of furniture or can't change your listening position....but it still seems that you'd advise not to to try to EQ out comb filtering issues. That leads me to the question, how do you identify comb filtering issues in room measurements....ie how do you know which parts of the frequency response to leave uncorrected? (I have an Anechoic EQ of a recently measured speaker by Amir - the JBL 308p and I've been debating a little on whether to EQ down a certain part of the in-room measurement because it's north of 300Hz (it's between 400-500Hz and maybe above the transition frequency).)

EDIT: here's the pic of my latest EQ, I do like it so far, it's Listening Window Anechoic EQ, no room EQ so far, I'm a bit loathe to EQ down the bass peaks because I know it will reduce the bass impact and it doesn't sound boomy or muddy at the moment, but it's the peak at 400-500Hz that I'm playing with the idea of EQ'ing down.....but if it's comb filtering I should leave it alone right?:
Trim Switch -2dB Listening Window Anechoic EQ effect on Room Measurment.jpg
 
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richard12511

richard12511

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Thread Starter #9
@richard12511 as mentioned in the other thread... Also, folks need to read a little closer :) Where does it that I say move everything out of the room? LOL! Attention to details matter.

The idea is not to move the furniture out of the room, it is to move anything between the mic and speakers out of the way that can cause comb filtering and anything around the microphone itself, like comb filtering off the chair/couch for example. We are concerned with midrange and high frequency comb filtering as the wavelengths are so long below 100 Hz that it does not have a real impact with objects in the way...

The fundamental issue is if one corrects for the “comb filtering” off the coffee table for example, then that correction is now embedded in the frequency response of the loudspeaker including it's off axis response. So if we correct for the comb filter off the coffee table, we have just coloured the off axis response of the loudspeaker. Here is a longer answer: https://audiophilestyle.com/forums/...kthrough/page/2/?tab=comments#comment-1032876

As mentioned in the link, recording, mixing and mastering engineers deal with this daily with mixing desks, etc. Mastering engineer Bob Katz has a nice comparison of the comb filtering he was getting at his mixing desk and found a unique to deal with it, including before and after measurements in his mastering book. It is a well known issue in studio world...

Why not try the try the experiment yourself, if you haven't already, and then compare the filters (measurement and listening) see which is better and report back.
Thanks. I guess I missed your response in the other thread. I wasn't necessarily saying you move everything out of the room, but I read on one of your blogs that you moved the coffee table(and maybe the couch?) over to the side of the room. I still need to read your longer answer, but just wanted to say thanks here first.

So it seems that the reason moving furniture away from the mic might be better is because I don't want Dirac trying to correct for the comb filtering that the furniture causes?

As for why I don't experiment? My couch is a huge L shaped 10 seater and moving it out of the way is very difficult, as I live alone, and I don't have room anywhere else to put it(I'd have to move the very large kitchen table out of the kitchen and then move the couch into the kitchen(it's all one big room). I figured I'd ask here first to gain a better understanding. I've got a couple speakers coming in in the next few days and I'll be experimenting a bunch with Dirac, SAM, and potentially a Windows OS solution.
 

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richard12511

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Thread Starter #10
After reading your longer reply, it seems like it might be worth it to experiment moving the couch over to the side before taking measurements. I may have to hire help, which is kinda why I started this thread(to avoid wasting time and money based on an incomplete understanding on my part).
 

Robbo99999

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#11
Thanks. I guess I missed your response in the other thread. I wasn't necessarily saying you move everything out of the room, but I read on one of your blogs that you moved the coffee table(and maybe the couch?) over to the side of the room. I still need to read your longer answer, but just wanted to say thanks here first.

So it seems that the reason moving furniture away from the mic might be better is because I don't want Dirac trying to correct for the comb filtering that the furniture causes?

As for why I don't experiment? My couch is a huge L shaped 10 seater and moving it out of the way is very difficult, as I live alone, and I don't have room anywhere else to put it(I'd have to move the very large kitchen table out of the kitchen and then move the couch into the kitchen(it's all one big room). I figured I'd ask here first to gain a better understanding. I've got a couple speakers coming in in the next few days and I'll be experimenting a bunch with Dirac, SAM, and potentially a Windows OS solution.
With an item of furniture that large you'd kinda think you'd have to leave it in the room for the measurement otherwise it would change things so much if you removed it that it would actually change the real sound you'd hear from the speakers regardless of whether or not it would solve comb filtering measurement issues......just using my imagination here rather than talking from experience. (Although I bet you'd want to take that little table out of the room based on what mitchco just said - that's between the speaker & you, and looks like a little piece of furniture that might just cause an anomaly at one position, but I'll wait to see what mitchco says as I'm using my imagination again).
 

andreasmaaan

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#12
Personally, I would not measure too close to the back of a couch or listening chair. Your brain will be used to processing the audio with the couch/chair you're sitting on as part of the scene. You won't want to alter the direct sound to compensate for it IMHO. So I'd move the couch back a bit (maybe not completely out of the way) when taking the measurement.

(This is not a hard and fast rule btw, just a casual opinion.)
 

mitchco

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#13
@richard12511 As mentioned in the other thread:

To my ears a correction filter developed without the coffee table during measurement and replaced for listening sounds more natural when I move around on the couch. I.e. the direct sound is flat and the comb filter sounds as it should. But "baking" the comb filter into a correction filter, no matter how many angles (i.e. mic locations) are covered, sounds to my ears, coloured, especially off axis. As mentioned at the end of my comment link above: There are no hard and fast rules, and I encourage folks to experiment.

So if you can't move the couch, you could put wool blankets, or what have you, on the couch near where the mic is to reduce the comb filtering effects. Same with the coffee table if you don't want to move it, but I remove mine and slide the couch out of the way as I have room to do so and it is easy to move. Other folks situation is different. But to be clear the couch is still in the room ;-)

@Robbo99999 I love REW, have been using it for over a decade and still use it daily. But it is not classified as "room eq" and there are differences. As brief as I can describe the major differences and approach: https://www.audiosciencereview.com/...udio-monitor-review.10897/page-44#post-344825 Looking at the REW measurement of the correction at the end of the post, one can see that below the room's transition frequency, the low frequency response is smooth and the low frequency reflections are mitigated by the excess phase correction employed by the room eq. Above the transition frequency, we are letting in the room reflections, but the direct sound frequency response (i.e. envelope) is still smooth. There is a lot to unpack there...
 
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richard12511

richard12511

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Thread Starter #14
Personally, I would not measure too close to the back of a couch or listening chair. Your brain will be used to processing the audio with the couch/chair you're sitting on as part of the scene. You won't want to alter the direct sound to compensate for it IMHO. So I'd move the couch back a bit (maybe not completely out of the way) when taking the measurement.

(This is not a hard and fast rule btw, just a casual opinion.)
Pushing it back up against the back subwoofer wouldn't be too hard. I could do that by myself.
 

Robbo99999

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#15
@richard12511 As mentioned in the other thread:

To my ears a correction filter developed without the coffee table during measurement and replaced for listening sounds more natural when I move around on the couch. I.e. the direct sound is flat and the comb filter sounds as it should. But "baking" the comb filter into a correction filter, no matter how many angles (i.e. mic locations) are covered, sounds to my ears, coloured, especially off axis. As mentioned at the end of my comment link above: There are no hard and fast rules, and I encourage folks to experiment.

So if you can't move the couch, you could put wool blankets, or what have you, on the couch near where the mic is to reduce the comb filtering effects. Same with the coffee table if you don't want to move it, but I remove mine and slide the couch out of the way as I have room to do so and it is easy to move. Other folks situation is different. But to be clear the couch is still in the room ;-)

@Robbo99999 I love REW, have been using it for over a decade and still use it daily. But it is not classified as "room eq" and there are differences. As brief as I can describe the major differences and approach: https://www.audiosciencereview.com/...udio-monitor-review.10897/page-44#post-344825 Looking at the REW measurement of the correction at the end of the post, one can see that below the room's transition frequency, the low frequency response is smooth and the low frequency reflections are mitigated by the excess phase correction employed by the room eq. Above the transition frequency, we are letting in the room reflections, but the direct sound frequency response (i.e. envelope) is still smooth. There is a lot to unpack there...
Hi mitchco, thanks for the response, had a quick read of your link where you go into more detail re RoomEQ, I'll have to absorb that when it's not so late in the day.

About the bit I bolded in your post, at first I thought you were referring to my screenshot of my in room measurement, but then realised you were referring to the post you linked me. Do you have any quick advice for me based on the measurement I showed you and the questions I asked re the relevance of EQ'ing down the peak at 400-500Hz, and how to identify comb filtering in a room measurement? I believe the link you linked me might answer that broadly, but like I said I'd have to absorb that tomorrow, but asking the question in the previous sentence in case your link doesn't cover those points.
 

win

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#16
You just have to be careful about putting the mic close to any surface really, but especially a back wall would be bad, you'll get exaggerated bass in the recording and hence EQ will deflate your bass unless your head is against the wall
 

onion

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#17
After reading your longer reply, it seems like it might be worth it to experiment moving the couch over to the side before taking measurements. I may have to hire help, which is kinda why I started this thread(to avoid wasting time and money based on an incomplete understanding on my part).
I've found moving the sofa even 50cm back or forth changes the frequency response of speakers/ subs quite dramatically, this for a 'small' room
 

Arnandsway

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#18
I read it's preferred to place the mic from any close surfaces, but what if the listening position is close to the back wall because the couch/chair is? I understand it's not perfect, but sometimes the only way.

What is the best practise then?
 

Snarfie

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#19
I had the same question regarding my placed drums as lamp an in the closet. When measuring with a sweep tone those drums resonate noticeable. Did ask a friend of mine who does (room) measurements on in an outdoor venues an concluded that it is OK because you want that be a part of the measurement.

 

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#20
How much impact does typical furniture - sofas, hi-fi gear, shelving, books etc. - have on frequencies below the Schroeder frequency?
 
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